1. Field of the Invention
The invention relates to a light source device which is used for a semiconductor lithography device, surface activating, precision machining (perforation, cutting to size, grooving), perforation of a printed board, installation of nozzles in an inkjet printer, marking and the like. The invention relates especially to a light source device consisting of a solid state laser device which can be used as a replacement light source for an excimer laser.
2. Description of the Related Art
There has recently been a demand for an increase of image definition according to refinement of an integrated semiconductor circuit or the like. The wavelengths of the exposure source are therefore becoming shorter and shorter. An ArF excimer laser with a wavelength of 193 nm is regarded as definitive as a light source for semiconductor lithography for the coming generation.
It is therefore well known that a light source using the above described excimer laser has the following disadvantages:
(1) Since corrosive gas is used as a laser medium, the electrodes which form the main part of the laser, and the main parts such as a capacitor and the like, are often corroded and degraded. Therefore the cost for their maintenance is high.
(2) The laser gas is also soon degraded. Therefore the gas must be replaced upon each recording by 10xc2x0.
(3) There is a problem with respect to safety precautions since the corrosive gas leaks.
(4) The gas pipelines consist of stainless steel in order to preserve the laser power. The accessories therefore become expensive.
The inventors therefore have already proposed the above described light source device in which using a solid state laser device light with a wavelength of 193 nm is generated (JP-HEI 9-112346).
(a) Quintuple waves of the laser light which is emitted from a Ndxe2x80x94YLF laser light source are produced by means of a nonlinear optical crystal LBO, CLBO (the first coherent light beam has a wavelength of 209.4 nm).
xe2x80x83Furthermore double waves of the laser light which is emitted by a Ndxe2x80x94YLF laser light source are produced by means of a nonlinear optical crystal LBO and a difference frequency between these double waves and the laser light which is emitted by a semiconductor laser light source is produced by means of a photoparametric oscillator (the second coherent light beam has a wavelength of 2532.814 nm). Light with a frequency (193.4 nm) formed by the sum of the first and the second coherent light beams is produced by means of the nonlinear optical crystal CLBO (first embodiment in JP-HEI 9-112346).
(b) Quintuple waves of the laser light which is emitted by a Ndxe2x80x94YAG laser light source are produced by means of a nonlinear optical crystal LBO, CLBO (the first coherent light beam has a wavelength of 212.824 nm).
xe2x80x83Furthermore, double waves of the laser light which is emitted by a Ndxe2x80x94YAG laser light source are produced by means of a nonlinear optical crystal LBO and a difference frequency between these double waves and the laser light which is emitted by a semiconductor laser light source is produced by means of a photoparametric oscillator (the second coherent light beam has a wavelength of 2185.8206 nm). Light with a frequency (193.9 nm) formed by the sum of the first and the second coherent light beams is produced by means of the nonlinear optical crystal CLBO (second embodiment in JP-HEI 9-112346).
The light source device described above in (a) and (b) had the following defects:
(1) The disadvantage of phase mismatch of the nonlinear optical crystal CLBO (hereinafter called xe2x80x9cCLBO crystalxe2x80x9d) in the generation of the frequency formed by the sum of the first and the second coherent light beams.
xe2x80x83The CLBO crystal has the property of often producing hydrates. Here, as shown in FIG. 26, there is an absorption band in the wavelength range of greater than 1800 nm, i.e. in the vicinity of 2 microns.
xe2x80x83In the above described (a) and (b) therefore absorption of the second coherent light beam becomes large (in (a) the light with a wavelength of 2532.814 nm and in (b) the light with a wavelength of 2185.8206 nm).
Therefore it is regarded as a disadvantage that heat is generated within the CLBO crystal, that due to the heat formed the phase matching angle deviates in the process of generation of the summed frequency, that therefore a phase mismatch state arises and that the efficiency of wavelength conversion into the light with the summed frequency decreases. The phase mismatch and phase matching can be taken for example from the Japanese patent application HEI 8-312478 already proposed by the inventors.
Furthermore, there is the disadvantage that absorption of the resulting light with a wavelength of 193 nm causes heating of the CLBO crystal, that therefore a phase mismatch state in the above described manner arises, and that the efficiency of wavelength conversion into the light with the summed frequency decreases.
(2) Disadvantage of phase mismatch of the CLBO crystal when the first coherent light beam is produced
xe2x80x83In the second coherent light beam the basic waves from a Ndxe2x80x94YLF laser light source and a Ndxe2x80x94YAG laser light source are converted by a first nonlinear optical crystal into double waves, by a second nonlinear optical crystal into quadruple waves and by a third nonlinear optical crystal into quintuple waves.
xe2x80x83Here the crystals which can be used in practice as the third nonlinear optical crystal which is used as the last stage for generating the quintuple waves are a CLBO crystal and a BBO crystal.
xe2x80x83But for the two crystals it is considered a disadvantage that due to phase mismatch as a result of absorption (linear absorption or two-photon absorption) of the resulting quintuple waves essentially the efficiency of wavelength conversion into quintuple waves decreases.
As was described above, in the above described light source device it was considered disadvantageous that the nonlinear optical crystal in the generation of quintuple waves and of light with the summed frequency absorbs light and furthermore also fundamentally light with the summed frequency, that therefore the state of phase matching of the crystal changes, and that the efficiency of wavelength conversion drops (hereinafter the above described change of the state of phase matching of the crystal into the state of phase mismatch is called xe2x80x9cheat induced phase mismatchxe2x80x9d).
The invention was devised to eliminate the defects of the above described conventional light source device. Therefore the object of the invention is to devise a replacement light source with a simple arrangement for an ArF excimer laser in which light with a wavelength of roughly 193 nm can be produced with high efficiency without reducing the efficiency of wavelength conversion, and in which thus the degradation of beam quality is only little.
The above described object is achieved as claimed in the invention as follows:
(1) A light source device which comprises:
a solid state laser light source which produces basic laser light with a wavelength of greater than or equal to 1000 nm and less than or equal to 1800 nm;
a means for producing a harmonic which produces a harmonic of the above described basic laser light;
a coherent light source which is excited by the above described harmonic; and
a means for producing a summed frequency which produces laser light with a summed frequency with a wavelength of roughly 193 nm from the basic laser light which is emitted from the above described solid state laser light source, and from the coherent light which is emitted from the above described coherent light source.
(2) A light source device which comprises:
a first solid state laser light source which produces first basic laser light with a wavelength of greater than or equal to 1000 nm and less than or equal to 1800 nm;
a second solid state laser light source which produces second basic laser light with a wavelength of greater than or equal to 1000 nm and less than or equal to 1800 nm;
a means for producing a harmonic which produces a harmonic of the above described second basic laser light;
a coherent light source which is excited by the above described harmonic;
a means for producing a summed frequency which produces laser light with a summed frequency with a wavelength of roughly 193 nm from the first basic laser light which is emitted from the above described first solid state laser light source, and from the coherent light which is emitted from the above described coherent light source; and
a timing circuit which controls the timing of the oscillation between the first solid state laser light source and the second solid state laser light source such that the first basic laser light and the coherent light are incident essentially at the same time on the means for producing a summed frequency.
(3) In (1) and (2) the angle between the basic laser light which is emitted from the solid state laser light source and the coherent light which is emitted from the coherent light source is fixed at greater than 0 degrees, the two types of light being incident on the means for producing a summed frequency.
(4) A light source device which comprises:
a solid state laser light source which produces basic laser light with a wavelength of greater than or equal to 1000 nm and less than or equal to 1800 nm using a solid state crystal which is doped with neodymium ions;
a first means for producing a harmonic which produces a harmonic of the basic laser light which is emitted from the solid state laser light source;
a photoparametric oscillator which is excited by the above described harmonic;
a second means for producing a harmonic which produces a harmonic of the laser light which is emitted from the above described photoparametric oscillator; and
a CLBO crystal on which the basic laser light emitted from the solid state laser light source as well as the harmonic of the laser light of the photoparametric oscillator which is emitted by the second means for producing a harmonic are incident, and which produces light with a summed frequency with a wavelength of roughly 193 nm.
(5) A light source device which comprises:
a first solid state laser light source which produces basic laser light with a wavelength of greater than or equal to 1000 nm and less than or equal to 1800 nm using a solid state crystal which is doped with neodymium ions;
a second solid state laser light source,
a first means for producing a harmonic which produces a harmonic of the basic laser light which is emitted from the above described second solid state laser light source;
a titanium-sapphire laser light source which is excited by the above described harmonic;
a second means for producing a harmonic which produces a harmonic of the laser light which is emitted from the above described titanium-sapphire laser light source;
a CLBO crystal on which the basic laser light emitted from the first solid state laser light source as well as the harmonic of the laser light of the titanium-sapphire light source which is emitted by the second means for producing a harmonic are incident, and which produces light with a summed frequency with a wavelength of roughly 193 nm and
a timing circuit which controls the timing of the oscillation between the first solid state laser light source and the second solid state laser light source such that the basic laser light from the first solid state laser light source and the harmonic of the laser light from the titanium-sapphire light source which is emitted from the second means for producing a harmonic coherent light are incident essentially at the same time on the CLBO crystal which produces the above described light with a summed frequency.
(6) A light source device which comprises:
a solid state laser light source which produces basic laser light with a wavelength of greater than or equal to 1000 nm and less than or equal to 1800 nm;
a means for producing a harmonic which produces a harmonic of the above described basic laser light;
a coherent light source which is excited by the above described harmonic;
a first means for producing a summed frequency which produces the first light with a summed frequency from the basic laser light which is emitted from the above described solid state laser light source, and from the coherent light which is emitted from the above described coherent light source; and
a second means for producing a summed frequency which produces the second light with a summed frequency with a wavelength of roughly 193 nm from the basic laser light which is emitted from the above described solid state laser light source, and from the light with a summed frequency from the above described first means for producing a summed frequency.
(7) A light source device which comprises:
a first solid state laser light source which produces the first basic laser light with a wavelength of greater than or equal to 1000 nm and less than or equal to 1800 nm;
a second solid state laser light source which produces the second basic laser light with a wavelength of greater than or equal to 1000 nm and less than or equal to 1800 nm;
a means for producing a harmonic which produces a harmonic of the above described second basic laser light;
a coherent light source which is excited by the above described harmonic;
a first means for producing a summed frequency which produces the first light with a summed frequency from the first basic laser light which is emitted from the above described first solid state laser light source, and from the coherent light which is emitted from the above described coherent light source; and
a second means for producing a summed frequency which produces the second light with a summed frequency with a wavelength of roughly 193 nm from the first basic laser light which is emitted from the above described first solid state laser light source, and from the light with a summed frequency from the above described first means for producing a summed frequency; and
a timing circuit which controls the timing of the oscillation between the first solid state laser light source and the second solid state laser light source such that the first basic laser light and the coherent light which is emitted from the above described coherent light source are incident essentially at the same time on the first means for producing a summed frequency.
(8) In (4) and (5) the solid state laser light source is formed from a Ndxe2x80x94YVO4 laser light source or a Ndxe2x80x94YAG laser light source or a Ndxe2x80x94YLF laser light source. The angle of incidence of the basic laser light incident on the CLBO crystal and of a third harmonic of the laser light of the above described photoparametric oscillator or the above described titanium-sapphire light source is selected such that the angle of reflection "THgr"ooe of the CLBO crystal as the means for producing a summed frequency with respect to its crystal axis lies in the following range:
77.4xc2x0xe2x89xa6"THgr"ooexe2x89xa690xc2x0
(9) In (1), (2), (3), (4), (5), (6), (7) and (8) there is a wavelength stabilization means which stabilizes the wavelengths of the light emitted from the coherent light source.
As was described above, as claimed in the invention a replacement light source for a ArF excimer laser can be obtained which has a simple arrangement and in which the degradation of the beam quality is only little. Furthermore the basic laser light emitted from the solid state laser light source can be introduced without attenuation into the means for producing a summed frequency. Thus it becomes possible to increase the conversion efficiency in the means for producing a summed frequency.
In addition, as claimed in the invention the light which is incident on the means for producing a summed frequency has longer wavelengths than the quintuple waves (wavelengths: 213 nm) of the light emitted from a Ndxe2x80x94YAG laser light source or quintuple waves (wavelength: 209.4 nm) of the light emitted from a Nd:YLF laser light source. Therefore the drop in conversion efficiency as a result of phase mismatch can be reduced compared to that in the prior art.
Since furthermore the wavelength of the basic laser light is greater than or equal to 1000 nm and less than or equal to 1800 nm, and since when using a CLBO crystal as the means for producing a summed frequency therefore the wavelength does not lie in the range of roughly 2 microns in which the absorption band of the CLBO crystal is present, the efficiency of wavelength conversion can be increased and the heat-induced phase mismatch can be made smaller by the means for producing a summed frequency than in the prior art.
In addition, by executing vector-phase matching the allowable width of the angle can be increased and the decrease of the conversion efficiency as a result of the heat-induced phase mismatch can be reduced.